This invention relates to a method of laser lithotripsy and more particularly to a method of laser lithotripsy using stretched Q-switched pulse solid-state lasers.
The treatment of renal lithiasis has advanced dramatically (C. G. Chaussy, G. J. Fuchs, "Extracorporeal Shockwave Lithotripsy", Monogr. Urol. 8:80 (1987); J. W. Segura et al., "Percutaneous Lithotripsy", J. Urol. 30:1051 (1983); J. W. Segura, D. H. Bagley, H. W. Schoenberg et al., "Transurethral Removal of Large Ureteral and Renal Pelvic Calculi Using Urethroscopic Ultrasonic Lithotripsy", J. Urol. 130:31 (1983) since a decade ago when Fair outlined the basic concept (H. D. Fair, "In Vitro Destruction of Urinary Calculi by Laser-Induced Stress Waves", Medical Instrumentation 12(2):100 (1978)). The development of percutaneous access to the kidney and "endorologic" destruction of kidney stones was followed closely by the development of extracorporeal shock wave lithotripsy (ESWL). The combination of these techniques has markedly decreased the need for open surgical removal of renal stones and ureteral stones. There are currently a number of techniques for treating stones within the ureter including ureteral cathertization, stone basketing, and ultrasonic lithotripsy (C. Chaussy, G. Fuchs, R. Kahn et al., "Transurethral Ultrasonic Ureterolithotripsy Using a Solid Wire Probe", Urology 29:531 (1987). The latter, although effective requires dilation of the distal ureter for access to the stone. Ureteral dilation can be traumatic and may lead to ureteral injury.
The most promising new technology for ureteral stone fragmentation is laser lithotripsy using a pulsed laser (G. M. Watson and J. E. A. Wickham, "Initial Experience with a Pulsed Dye Laser for Ureteric Calculi", Lancet 1357 (1986). Optical fiber delivery systems for pulsed lasers having diameters as small as 200 microns can transmit enough energy to fragment stones. The concomitant development of very small uretheroscopes now permits atraumatic urethroscopy in combination with the pulsed laser stone fragmentation.
The pulsed dye laser, which emits pulses of approximately 1 .mu.s in duration, have been used successfully in clinical lithotripsy procedures. Dye lasers are,, however, less favorable than solid state lasers from the standpoint of size, reliability, ease of use, and ease of maintenance. Despite the general preference of solid state lasers over dye lasers from this standpoint, comparatively little success has been obtained with them in the lithotripsy application. Studies have shown that these lasers typically emit pulses either too short not to destroy the critical optical fiber or too long to be effective in breaking up the calculi.
Techniques have been developed in order to limit damage to tissues of the urinal tract by the laser beam. In one such technique developed for and used in dye laser lithotripters, the back scattered light, which is generated in the targeted material and passes back through the optical fiber, is used to preempt the continued development of the laser pulses before a plasma can be created in the event that the targeted material is not that of calculi. This so called "stone recognition system" has proved very effective in reducing damage to normal tissue.